1. Field of the Invention
The present invention relates to an ink composition, an inkjet recording method, and a printed article produced therewith.
2. Description of the Related Art
There are many image-recording methods for forming an image on a recording medium such as paper based on image data signals, including those by an electrophotographic process, sublimation or fusion heat-transfer process, and inkjet process. For example, the inkjet process is advantageous in that it allows printing in a cheaper device at a lower running cost, because it forms an image directly on a recording medium by ejecting ink only in a required image region and thus uses the ink more efficiently. In addition, the inkjet process is also less noisy and thus advantageous as an image-recording method.
According to the inkjet method, it is possible to print not only on regular paper but also on a non-absorptive recording medium such as a plastic sheet or a metal plate. However, increased speed at the time of printing and increased image quality are key issues, and it is a property of the inkjet method that the time required for drying and curing droplets after printing greatly affects the productivity of printed materials and the sharpness of printed images.
As one of the inkjet methods, there is a recording method using an inkjet recording ink that is curable by irradiation of radiation. According to this method, by curing ink droplets by irradiating radiation immediately after or after a fixed time after the ink is ejected, the productivity of printing can be increased, and sharp images can be formed.
By increasing the sensitivity of the inkjet recording ink which is curable by irradiation with a radiation ray such as ultraviolet light, the ink has higher curability with respect to radiation rays, which brings about many benefits such as improvement in inkjet recording efficiency, reduction in power consumption, prolongation of the lifetime of a radiation ray generator owing to a decrease in the load, and prevention of volatilization of low molecular weight substances caused by insufficient curing. Further, the increase in the sensitivity particularly increases the strength of the image formed using the inkjet recording ink.
Such an inkjet method for curing by radiation such as ultraviolet rays has been drawing attention from the standpoints of relatively less odor, quick drying properties, and a capability of recording onto a non-ink-absorptive recording medium. Ultraviolet ray curable ink compositions for inkjet using radical polymerization are disclosed in Japanese Patent Application Laid-Open (JP-A) No. 63-235382, JP-A No. 3-216379, JP-A No. 5-214280, Japanese Patent Application Publication (JP-B) No. 6-21256, and JP-B No. 6-62905.
In addition, in order to attain inkjet ejection stability, for the purpose of reducing the surface tension of an inkjet ink, inkjet inks using silicone derivatives (for example, see Japanese National Phase Publication No. 2001-525479 and JP-A No. 5-222198), an inkjet recording method, and a printed article using the inkjet inks are disclosed.
However, these inks (compositions) are insufficient in rubfastness and blocking resistance of images formed by ejecting the inks, and have been unable to attain sufficient compatibility between the ink ejection stability and the curing properties of resultant images.